From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D971174040 for ; Wed, 21 May 2025 13:27:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747834043; cv=none; b=GPj3kZbfY89IiamEctB2HuOXWNuvRoySIP0IV10TpyXBHUQLWAcNHVUTbpktceEuOri0ypS8wAkwwL/dJl9ABsQfDXy6ZVyzOkKN8Ll8py80oZup/IKPCxo13ZM/ZPL86qDzAJlO4pF29Bx0j1ALKwqu0CMFkykvY6SbF6ZQaE4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747834043; c=relaxed/simple; bh=xjFng9sdMzEFMX072tCQ9nsFr/cdpH/wI9japwTPBBw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ADdFrtt9/CnximiieKWoS1texRKYEQuE9qlv6oCH1oWtWKc8msJhPGbmRgNKFpiCv0t4xCiCR1i/ZvolDoPyeN7cRC/K4cjYDzhEi1nbFplui2Xa0vbuBZ20BZbvg1di+k0uHbGQLUM3LSQ2UfX2uh6w/xIjZzuAWQmK2O5Lygs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=jv+kAAAq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="jv+kAAAq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 67908C4CEE4; Wed, 21 May 2025 13:27:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1747834043; bh=xjFng9sdMzEFMX072tCQ9nsFr/cdpH/wI9japwTPBBw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jv+kAAAqFeIsWMj8Fom2dnW0M/SGE7/3t5nV5bOsMFtR8UAR5LGitH2MvyMyAxldl LakRF6XRNDeh3wDkqCbzkdBkDoqHjboCtagxWQ/2vOjBa5CCkpgJXQuMWjmEpot0c4 iztYMnZk0NZ/TSRxPsNgKps4CaSf6Wg0aPc4u314= Date: Wed, 21 May 2025 15:27:19 +0200 From: Greg Kroah-Hartman To: Sakari Ailus Cc: Andy Shevchenko , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] container_of: Document container_of() is not to be used in new code Message-ID: <2025052138-carport-applaud-61b8@gregkh> References: <20250520103437.468691-1-sakari.ailus@linux.intel.com> <2025052000-widen-lip-350b@gregkh> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, May 20, 2025 at 10:09:18PM +0000, Sakari Ailus wrote: > Hi Greg, > > On Tue, May 20, 2025 at 04:30:19PM +0200, Greg Kroah-Hartman wrote: > > On Tue, May 20, 2025 at 05:16:45PM +0300, Andy Shevchenko wrote: > > > On Tue, May 20, 2025 at 01:34:37PM +0300, Sakari Ailus wrote: > > > > There is a warning in the kerneldoc documentation of container_of() that > > > > constness of its ptr argument is lost. While this is a faible suggestion > > > > container_of_const() should be used instead, the vast majority of new code > > > > still uses container_of(): > > > > > > > > $ git diff v6.13 v6.14|grep container_of\(|wc -l > > > > 646 > > > > $ git diff v6.13 v6.14|grep container_of_const|wc -l > > > > 9 > > > > > > > > Make an explicit recommendation to use container_of_const(). > > > > > > > > Signed-off-by: Sakari Ailus > > > > --- > > > > Hi Greg, Andy, > > > > > > > > I guess we generally agree the additional constness check in > > > > container_of_const() is useful, but adding the same check to > > > > container_of() generates warnings -- there are some errors, too -- such as > > > > this one currently: > > > > > > > > In file included from /home/sailus/src/linux/include/linux/bcma/bcma.h:14, > > > > from /home/sailus/src/linux/arch/x86/kernel/early-quirks.c:17: > > > > /home/sailus/src/linux/include/linux/ssb/ssb.h: In function ‘dev_to_ssb_dev’: > > > > /home/sailus/src/linux/include/linux/ssb/ssb.h:291:14: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers] > > > > 291 | wrap = container_of(dev, struct __ssb_dev_wrapper, dev); > > > > | ^ > > > > > > > > As noted above, 646 new missing constness checks were introduced through > > > > container_of() macro use during the 6.14 cycle alone. Most of these are > > > > likely harmless, but with so many new users some are bound to be ignoring > > > > constness. > > > > > > > > Once the warnings from bad container_of() use are worked out in a way or > > > > another, the constness check could be added to the container_of() macro > > > > and the current container_of_const() be dropped altogether. > > > > > > > > If this patch is accepted, I'll see how to add a warning on container_of() > > > > to checkpatch.pl. > > > > > > Hmm... Wouldn't be better to fix non-const cases and add the const check, etc > > > to the container_of() instead of doing these comments? > > > > Yes, fixing up the existing places where it is broken would be best, how > > many of them are there now? > > Adding constness check for container_of(), with my partial build on x86-64 > I'm getting 893 such warnings. A fair number are probably duplicates or > repeat of the same pattern, but also the compilation didn't succeed -- > there were multiple compilation failures. So who is going to do that work? I just did it for drivers/usb and it was pretty trivial, just declaring "do not use this!" feels like the easy way out, absolving yourself from any responsibility here :) thanks, greg k-h